And the hardest thing I've ever done to myself was, at one point while playing through Half Life 2 I saved a game so that I would near immediately die, somehow after a large amount of retries I was able to get kill 15 combine and survive a Hunter Chopper attack, all without getting hit.

..goddamned fan boat level...

i know exacly what you mean. only my experience is in HL1, if you played it you know the like blade headed thing that attacks you when you make sounds and its in the reactor thingy? well i had 5 health while trying to get through it, and its literally impossible, i could not get by.